In the field of processing of wafers for the production of semiconductor devices, the wafers must be processed in a vacuum environment for such steps as ion implantation. Yet production-line requirements dictate rapid movement of the wafers from one work station to another, and therefore between vacuum environments and atmospheric environments. Such movement of the wafers has required the use of valve mechanisms which should be able to open and close so as to provide vacuum-tight seals, and which also should be made of such materials and so constructed that pollution of the vacuum by escape of particles, etc. is kept to a minimum. Conventional valve mechanisms inherently generate unwanted particles as a result of friction between the moving parts as the valve is opened and closed.
Prior art valves which close an aperture have an aperture-closing member the movement of which against the aperture to be closed involves some sliding contact. While perfectly acceptable for many applications, such sliding contact has undesirable effects in vacuum environments, particularly the high-vacuum, clean atmosphere required for semiconductor wafer manufacture. Recently attempts have been made to design valves suitable for such high-vacuum, clean environments. One such attempt is the so-called "monovat" slit valve manufactured by VAT Aktiengesellschaft in Haag, Switzerland. This monovat valve attempts to improve valve structure by causing the aperture-closing member to move in only one dimension: the apertured member is stepped in the vicinity of the aperture, and the motion of the aperture-closing member is across, rather than against, the aperture, sealing partly against one seat on the inner wall of the aperture and partly against another seat on the exterior wall of the aperture. Another such attempt is shown in PCT patent publication No. W090/08275 published Jul. 26, 1990 entitled "Valve Body for Non-sliding Gate Valve" and Japanese patent publication No. 63/254275 published Oct. 20, 1988 entitled "Sliding-free High Vacuum", both in the name of Irie Koken Kabushiki Kaisha. These patent publications disclose valve structures wherein the aperture-sealing mechanism is completely separate from the aperture-covering mechanism and uses compressed air directly to seal the gate against the aperture.
Another gate valve is disclosed in U.S. Pat. No. 4,721,282 to Shawver et al. As in Applicant's device, the Shawver et al. device separates translational movement of the gate from lateral movement thereof; i.e. it separates the slot-covering motion irom the sealing motion. However, the mechanism employed differs from Applicant's mechanism in the following respects.
To seal the gate, Shawver et al. employs a link assembly which pushes a shaft, supported in cantilever, so that a gate member at the end thereof is pushed against the slot. Far from relying on springiness of the shaft, it would seem that Shawver et al. relies on stiffness of the shaft, since the gate itself is rotatably supported on the shaft by a pin (bearing no reference numeral). It would seem that the structure of the cam followers 56 in the guide tracks 58 may be the portion best adapted to provide springiness, although it may be that the O-ring alone provides adequate yield. Column 2 line 43 and column 5 line 5 refer to "over center" travel. This would suggest that any springiness is of a minor nature, easily provided by the O-ring.
Valves of the type of the present invention are used in various applications. One such application may be illustrated by U.S. Pat. No. 4,730,976, the disclosure of which is incorporated herein by reference. FIGS. 3A, 3B and 3C of that patent illustrate use of the article transfer device claimed in that patent to transfer wafers from one place to another: namely, from each of two elevators to some wafer-processing station. When such an article-transfer device is used in a vacuum environment, the valves of the invention may be used between the various components shown in said Figures: e.g. between each of the elevators and the article-transfer device, and between the article-transfer device and the work-station. Such use in a vacuum environment is shown in FIG. 4 of said patent, and valves of the type of the present invention may be used between the first elevator 51 and the vacuum chamber 61, and between the vacuum chamber 61 and the second elevator 53.